1. Field of the Invention
The present invention relates to a crochet machine for warp knitting workings, of the type comprising a bearing base having two side standards, a plurality of needles disposed consecutively in side by side relation along a needle bar extending between the side standards, a plurality of eye-pointed needles disposed consecutively in side by side relation parallelly to the needle bar and in front of the needles and each arranged to engage a respective warp thread, longitudinal-movement means of the needles to impart to the needles a reciprocating movement along their longitudinal extension, and transverse-movement means of the eye-pointed needles to impart to the eye-pointed needles a reciprocating motion substantially parallel to the longitudinal extension of the needle bar.
2. Prior Art
It is known that in warp knitting crochet machines, such as crochet galloon looms, formation of the article of manufacture takes place at a needle bar having a horizontal extension and rigidly supported at the respective opposite ends by two side standards being part of the machine base. Operating on the needle bar is a plurality of needles disposed consecutively in side by side relation and simultaneously reciprocated in the direction of their longitudinal extension. Operating in front of the needles is a plurality of eye-pointed needles disposed consecutively in side by side relation parallelly to the needle bar and supported by a guide bar engaged through the standards so that it can slide and also carry out an angular oscillation on its longitudinal-extension axis. The guide bar is submitted to the combined action of transverse-movement means imparting to the eye-pointed needles a reciprocating motion in a direction parallel to the needle bar and angular-oscillation means by which the eye-pointed needle ends perform a reciprocating motion in a substantially vertical direction, alternately moving to a higher level and a lower level than the needles themselves.
The needle and eye-pointed needle movements are synchronized so that when the needles are at an advanced position towards the eye-pointed needles, the latter are at a raised position and perform a translation movement, each moving from one side to the other of at least one respective needle. During this step the warp thread of each eye-pointed needle is arranged astride the needle, in order to be engaged by the hook-shaped portion provided at the needle end.
When the needles move backward from the advanced position, the warp thread engaged in the hook portion of each needle forms a loop which is guided through the knitting stitch loop formed in the preceding operating cycle, whereas the stitch itself, retained by the needle bar, is discharged from the needle end when said needle is about to reach the end-of-stroke position in its backing off step. Meanwhile, the eye-pointed needles are brought to a slightly lower level than the needles. When the needles are about to be brought back to the advanced position, the eye-pointed needles are translated horizontally in a direction opposite to the horizontal movement previously performed, so that the warp threads form new knitting stitches sliding along the needles during the advancing step thereof. When the needles come close to the advanced position again, the eye-pointed needles again take a slightly higher level than the needles, to start a new knitting cycle.
Cooperation between the needles and eye-pointed needles gives rise to a sequence of knitting stitches, forming a plurality of parallel chains gradually descending from the needle bar.
In most cases, the chains are also interlaced with the weft threads carried by respective threading tubes operating above the needles and disposed consecutively in side by side relation parallelly to the needle bar. The threading tubes are supported by one or more carrier slide bars the opposite ends of which are slidably guided through lifting plates in turn connected to the base standards so as to slide in a vertical direction.
Each carrier slide bar is submitted to the action of respective horizontal-movement means imparting to each threading tube a reciprocating motion parallel to the needle bar extension. In addition, the carrier slide bars are simultaneously set in operation for carrying out a reciprocating oscillation in a vertical direction upon command of a kinematic mechanism acting on the lifting plates.
Operation of the carrier slide bars is coordinated with that of the needles and eye-pointed needles, so that each weft thread is selectively laid down astride one or more needles in order to pass under said needles when the latter reach the return end of stroke and start their advancing movement towards the eye-pointed needles again.
The weft thread placed under the needles will be interlooped into the knitting stitches formed by the warp threads in the subsequent operating cycle.
That being stated, it is pointed out that within the development and improvement scope of the warp knitting machines for meeting the increasing market requirements, many efforts have been made in an attempt to increase the productivity of said machines.
In this connection, devices have been also developed that control the horizontal movement of the individual carrier slide bars by means of respective electric stepping motors, operation of which is managed by an electronic control unit.
Such a control device is described in the European Patent Application EP 0 533 603, in the name of the same inventor.
Operation of the carrier slide bars by stepping-motor control devices has enabled operating speeds even in the order of 1200 rpm to be reached. However, it has been found that, due to the capacity of the stepping-motor control devices, even higher speeds could be reached, also in the light of possible future developments. Furthermore, speeds in the order of 1200 rpm can be achieved only on machines the needle bar of which is of a relatively reduced length, in the order of 400 mm. In knitting machines provided with a longer needle bar, of 600/800 mm for example, the operating speed is to be correspondingly reduced, thereby greatly reducing the productivity difference that these machines would potentially have as compared with those having a shorter needle bar.
It should be also noted that the greatest restrictions are found on those machines that, due to production requirements, are equipped with a great number of carrier slide bars disposed in a fan configuration between the lifting plates, to cause the ends of the respective threading tubes to converge as much as possible close to a common alignment direction.
Based on the above considerations it has been found that presently the greatest constraint to productivity in crochet knitting machines is due to the fact that, at high speeds, the carrier slide bars inevitably tend to bend in the longitudinal extension direction, by effect of the important shakings undergone as a result of the vertical reciprocating movements. These bending deformations bring to an imprecise positioning of the individual carrier slide bars with respect to the needles, and sometimes even to mechanical interferences, which will bring about risks of damages and/or breakages of these components.
Due to the lack of available spaces around the carrier slide bars, appropriate modifications to the structure configuration of said bars aiming at increasing the moment of inertia of same in their longitudinal bending plane, practically cannot be proposed.
In addition, said bending phenomena give rise to several other drawbacks, such as an early and anomalous wear of the bushes designed to guide the carrier slide bar ends through the lifting plates, for example. Another undesired effect of the carrier slide bar deflection is represented by noise, in that at high operating speeds noise tends to reach the limits established by the regulations in force.